Appendix 1 – Predicted changes to Tasmania’s climate

To help us understand how climate change is predicted to affect Tasmania, the internationally regarded Climate Futures for Tasmania project was undertaken by the Antarctic Climate and Ecosystems Cooperative Research Centre, based at the University of Tasmania.

The project provides the first fine-scale climate information for Tasmania by downscaling six global climate models with two emission scenarios (high emissions scenario - A2 and lower emissions scenario - B1) to generate climate information from 1961 to 2100.

This information helps us understand the changes at a local and regional level in Tasmania.

Increasing temperature

Mean or average temperature in Tasmania has increased by more than 0.5°C since 1950, with a higher trend in the north-east than in the rest of the State. The increase has been greater for minimum temperatures (usually occurring overnight) than for maximum temperatures.

The projected rise in mean temperature is relatively uniform across Tasmania. There is more spatial diversity in the change in temperature in each season than in the annual change[59]. The spatial pattern of the trend in daily maximum temperature since 1961 is for greater change in the north-east and the interior, whereas daily minimum temperature has generally increased more on the north coast and less in the interior[60].

By 2100, Tasmania’s temperature is projected to rise by approximately 2.9°C under the Intergovernmental Panel on Climate Change (IPCC)’s ‘high emissions’ scenario (A2), and by approximately 1.6°C under the ‘low emissions’ scenario (B1)[61]. Tasmania’s projected temperature changes for both emissions scenarios are less than the projected Australian and global average temperature changes for the same period. This is largely due to the moderating influence of the Southern Ocean.

Changing rainfall and runoff

Tasmania experienced a downward trend in rainfall over the period 1970 to 1990[62] and this has continued as shown in the Figure 1 below. The largest changes in Tasmanian rainfall have been observed in autumn[63].

There is no significant change to projected total annual rainfall over Tasmania under either the high emissions (A2) and low emissions (B1) scenarios. However, rainfall patterns across Tasmania and from season to season show significant changes under these emissions scenarios[66]. Projections show a steadily emerging pattern of increased rainfall over Tasmania’s coastal regions, and reduced rainfall over central Tasmania and in the north-west.

A slight increase is projected in the total amount of runoff in the State by 2100, although there is likely to be localised variations experienced. For example, runoff is projected to decrease markedly in the central highlands, which will impact on water catchments and therefore hydro-electric generation capacity in the region. Runoff is likely to increase, however, in the important agricultural regions of the Derwent Valley and the Midlands over the same period[67]. Changes in rainfall and runoff patterns may also impact on water quality and availability for irrigation and drinking uses[68].

Increasing frequency and severity of extreme events

Changes are expected to the frequency and severity of extreme weather events. Rainfall intensity and associated flooding is projected to increase across Tasmania, with longer dry periods in between heavy downpours. For example, St Helens in the State’s north-east, experiences a high rainfall event on average once every 200 years. This occurrence is projected to increase and become a once in 20 years event by 2100. The number of extreme wet days could also increase by up to 25 per cent in both the south-west and north-east of the State[69].

The occurrence of hot summer days and heat waves is also projected to increase. The largest increases in extreme temperature are projected to occur in the spring and autumn months, with increases of greater than 4°C. The number of heat waves (where maximum temperatures exceed 28°C for more than three consecutive days) at Launceston for example, is projected to increase progressively over the coming decades to twice per year on average. This is approximately four times more frequent than what is currently experienced[70].

Increasing temperature of surface waters

The surface waters off the east coast of Tasmania have warmed by approximately 2°C over the past 60 years. This is two to three times the global rate[71]. Ocean temperatures are projected to increase further as the warm East Australian Current is expected to extend south along the Tasmanian coast[72]. The observed strengthening of the East Australian Current is consistent with projections that Tasmanian waters could warm by another 2 to 3°C by 2070[73].

Sea level rise and storm surge

Predicted changes in sea levels vary from location to location due to a number of regional variations in ocean density and dynamics, such as:

thermal expansion, as water warms and expands in Spring and Summer, and cools and shrinks in Autumn and Winter[76]; and

changes to the ‘solid’ Earth and to the gravitational field resulting from changes in land ice mass gains and losses[77].

The IPCC Third Assessment Report 2001 (TAR) and Fourth Assessment Report 2007 (AR4) estimate a sea level rise of between 26 cm and 59 cm by 2100 for the ‘no mitigation’ scenario (A1FI). It is estimated that the contribution of melting ice sheets this century may also substantially increase the upper end of this estimate to 76 cm by 2095[78].

Around Tasmania, the largest storm surges occur on the south-east coast and the smallest on the northern coast. Sea level rise under the no mitigations scenario could lead to the water levels associated with a 1-in-100 year storm tide event occurring as frequently as once every 50 years by 2030[79].

Other changes

Tasmania can expect a number of other changes, including[80]:

an increase in relative humidity around the coasts and a decrease over inland, and high-altitude regions, with a different pattern in each season;

a reduction by approximately 50 per cent in the incidence of frost by the end of the century;

a decrease in chill hours at sites below 500 m elevation, but an increase in chill hours at higher elevation sites;

a modest increase in wind risk under a high emissions scenario of up to 25 per cent by 2090; and

an overall reduction of less than 5 per cent in solar radiation (sunshine), comprising a decrease on the east coast and an increase on the west coast.